using System.Collections.Generic;
public static void Main()
List<List<int>> List = new List<List<int>>();
List<int> SubList1 = new List<int> { 1 };
List<int> SubList2 = new List<int> { 2,3 };
List<int> SubList3 = new List<int> { 4,5,6 };
Console.WriteLine(List[0][0]);